1. Field of the Invention
The present invention relates to a UV-assisted advanced-ozonation water treatment system using ozone and UV light. More particularly, the present invention relates to a UV-assisted advanced-ozonation water treatment system using ozone and UV light for the purification of raw water to produce clear water, secondary sewage, industrial waste water, industrial waste, seepage through a landfill or such, and an advanced-ozonation module.
2. Description of the Related Art
The pollution of water by industrial wastewater and sewage has progressively grown worse in recent years, and environmental water pollution has become a significant social problem. It is indicated that water in the upper reaches of rivers, which are sources of clear water, contains hardly decomposable pollutants such as agricultural chemicals, dioxins and environmental hormones, in small concentrations. The pollution of lower reaches of rivers is more serious; lower reaches of rivers are polluted with various chemical substances including organic chloride detergents, agricultural chemicals, synthetic detergents and dyes. The pollution of seepage from landfills containing industrial and domestic wastes is in an extremely serious condition. Active efforts are being made for the development of environmental water conservation techniques. Efforts have been made for the development of techniques for activated carbon treatments, membrane processes, ozonation treatments and biological treatments. An advanced oxidation process (hereinafter abbreviated to “AOP”) using UV light, hydrogen peroxide, or a combination of UV light and hydrogen peroxide is a promising comprehensive process. FIG. 27 is a block diagram of assistance in explaining the advanced-oxidation process. Referring to FIG. 27, an advanced-oxidation water treatment system includes a water treating tank 51, a UV light source 54, a power supply 55 for supplying power to the UV light source 54, an ozone generator 56, an ozonized gas diffusing device 50 and a discharged-ozone decomposer 58. An ozonized gas is diffused in bubbles by the ozonized gas diffusing device 50 into water contained in the water treating tank 51. Then, the ozonized gas dissolves in the water. When the water containing the ozonized gas is irradiated with UV light, radical species having oxidizing power higher than that of ozone are produced in the water, and the radical species decompose hard-to-decompose substances that could not be decomposed by ozone. The advanced oxidation water treatment using ozone and UV light in combination is capable of achieving efficient decomposition, has improved deodorizing, decolorizing and sterilizing functions and is capable of achieving water purifying treatment without secondary waste.
Although the advanced-oxidation water treatment system shown in FIG. 27 purifies water effectively, pollutants to be decomposed cannot efficiently be decomposed if the quantity of ozone diffused into the water or the quantity of UV light emitted by the UV light source becomes insufficient due to the variation of the quality of the water being treated. If surplus ozone 57 is diffused into the water, the ozonized gas not dissolved in the water and remaining in the water treating tank needs to be decomposed by the discharged-ozone decomposer 58 and increases load on the discharged-Ozone decomposer 58. If a surplus quantity of UV light is emitted, the UV light source 54 consumes power uselessly and reduces the overall energy efficiency of the advanced-oxidation water treatment system. Organic substances and inorganic substances contained in the water adhere to the surface the UV-radiating wall of the UV light source 54 and reduce the UV transmittance of the UV-radiating wall. Consequently, the efficiency of decomposing pollutants contained in the water is reduced. Work necessary to clean the surface of the UV-radiating wall increases load the maintenance of the advanced-oxidation water treatment system.
If raw water to be treated contains seawater or an effluent containing ions of bromides that comes from a photographic plant, it is possible that bromic acid, which is a carcinogenic substance, is produced when the water is treated only by the advanced oxidation process using ozone and UV light in combination.